CPMK

CPMK (LET)

Let Subcommand

Compute the C_pmk process capability index for a variable.

This statistic computes the sample C_pmk process capability index of an industrial process and is defined as follows:
\( C_{pmk} = \frac {\min(ENGUSL - \bar{x},\bar{x} - ENGLSL)} {3 \sqrt{s^{2} + (\bar{x} - TARGET)^{2}}} \)

with TARGET, ENGLSL, ENGUSL and \( \bar{x} \) denoting the target engineering value, the lower engineering specification limit, the upper engineering specification limit and the sample mean, respectively. This capability index combines both precision and unbiasedness.

The C_pmk statistic can have values from 0 to infinity with values between 0.5 and 1 being typical.

The specification limits define the range within which a product is considered acceptable (values outside this range indicate that a product is defective).

LET <par> = CPMK <y>             <SUBSET/EXCEPT/FOR qualification>
where <y> is the response variable;
            <par> is a parameter where the computed CPMK is stored;
and where the <SUBSET/EXCEPT/FOR qualification> is optional.

LET A = CPMK Y1
LET A = CPMK Y1 SUBSET TAG > 2

The target and upper and lower specification limits must be specified by the user as follows:
LET TARGET = <value>
LET LSL = <value>
LET USL = <value>

Dataplot statistics can be used in a number of commands. For details, enter
HELP STATISTICS

None

None

CAPABILITY ANALYSIS	=	Perform a capability analysis.
CP	=	Compute a Cp process capability index.
CPK	=	Compute a Cpk process capability index.
CNPK	=	Compute a Cnpk process capability index.
CPM	=	Compute a Cpm process capability index.
CC	=	Compute a Cc process capability index.
CPL	=	Compute a Cpl process capability index.
CPU	=	Compute a Cpu process capability index.
CNP	=	Compute a Cnp process capability index.
CNPM	=	Compute a Cnpm process capability index.
CNPKM	=	Compute a Cnpkm process capability index.
PERCENT DEFECTIVE	=	Compute the percentage of defectives in a sample.
EXPECTED LOSS	=	Compute the expected loss of a sample.

Chen and Ding (2001), "A New Process Capability Index for Non-Normal Distributions," International Journal of Quality & Reliability Management, Vol. 18, No. 7, pp. 762-770.

Kaoru Ishikawa (1982), "Guide to Quality Control," Asian Productivity Organization, (chapter 13).

Quality Control

2015/04

 
SKIP 25
READ FURNACE.DAT X1 X2 X3 Y
LET TARGET = 550
LET LSL = 460
LET USL = 660
LET A = CPMK Y 
MULTIPLOT CORNER COORDINATES 5 5 95 95
MULTIPLOT 2 2
MULTIPLOT SCALE FACTOR 2
TITLE AUTOMATIC
CPMK PLOT Y X1
CPMK PLOT Y X2
CPMK PLOT Y X3
END OF MULTIPLOT